Manufacture of sheet material



Patented July 3, 1928.

UNITED STATES PATENT. OFFICE.

REED P.ROSE, OF JACKSON HEIGHTS, NEW YORK, ASSIGNOR TO GENERAL RUBBER COMPANY, OF NEW YORK N. Y., A CORPORATION OF NEW JERSEY.

MANUFACTURE OF SHEET MATERIAL No Drawing.

This invention relates to improvements in the manufacture of fibrous sheet materials, and particularly to the manufacture of such sheet materials which contain ingreclients adapted to impart specific properties not ordinarily possessed by sheets containing fibre alone. More particularly the invention relates to an improved method of securing an intimate relationship between 10 the fibres and these non-fibrous ingredients.

The invention comprises beating paper making fibre, mixing a dispersion of nonfibrous paper making ingredients therewith, and altering the electrical charge in the dispersion in such a Way to cause the dispersed particle to migrate towards and adhere to the fibres, and subsequently forming the product into sheets or slabs by paper making methods or by molding the wet, partially dry, or dry fibre.

As one illustration of a method of carrying out the invention, a paper making fibre is beaten in water in the usual way preparatory to the manufacture of paper. After the beating has progressed to a satisfactory degree for the manufacture of the desired sheet, I introduce an alkaline dispersion of rubber in water containing sodium resinate to the amount of 5% of the weight of the rubber. I then mix the dispersion of rubher with the suspension of fibres until an approximately uniform mixture is obtained. I may accomplish this in the beater by simply raising the beater roll and making it serve as an agitator or I may carry out the process in a tank fitted with a suitable stirring mechanism such as a stuff chest. After a uniform distribution is obtained I slowly add a dilute solution of paper makers alum. meanwhile continuing the agitation. \Vhen the liquor in the heater or st-ufi chest is clear, the dispersed material is substantially quantitatively deposited on the fibres. The alum solution is preferably less than 3% concentration. It is of course understood that the percentage of dispersed rubber may be varied considerably depending upon the properties which are desired. but a good practice is to add a total of 2050% of rubber dispersion based on the dr weight of the fibre.

Ihe treated fibres may now be passed to the stuff chestsF-and to the paper making machine and further handled in accordance Application filed December 2, 1926. Serial No. 152,312.

with the ordinary practice for making fibrous sheet or slab material.

I prefer to add the alum solution slowly and to continue the agitation meanwhile, for this secures an even distribution of the dispersed rubber on the fibres and serves to prevent the formation of aggregates of the rubber.

My invention is based upon the theory that finely divided particles including cellulose fibres bear a negative charge in either alkaline or acid suspension. It is known that soaps of monovalent or divalent metals, as for example the oleates, stearates, resi- Dates, and the like carry a comparatively high negative charge in alkaline solution, but reverse this charge to positive when in acid solution. It is also known that these soaps are excellent protective agents for dispersions of inert materials of almost any description including rubber, carbon black, graphite, waxes, parafiines, resins (synthetic or natural), Wood tars and pitches, etc. When dispersions containing for example sodium resinate as the protective agent are mixed with a suspension of fibres, the dispersed particles do not migrate towards the fibres for the reason that both particles and fibres bear the same charge. I have found that the addition of an acidic agent causes the negatively charged sodium resinate to become positively charged. Since the particles of the dispersion now carry a positive charge they will migrate towards the negatively charged cellulose fibres and become firmly attached thereto. By this procedure it is possible to obtain an almost quantitative retention of the dispersed ingredient by the fibres, as may be readily seen by the absence of cloudiness in the waste water. Owing to the fact that the charge on the cellulose fibre is relatively weak in comparison with the charge on the inert particles with their protective film of sodium resinate, the reversal of charge is preferably carried out with care, adding the acid solution in dilute form, and carrying out the addition slowly enough so that the isoelectric point is reached gradually. This guarantees that only a small charge, equal in magnitude to the charge on the fibre, is produced during the stage where the particles are migrating to the fibres. It is of course understood that when I refer to negatively charged particles and to reversing the charge on these, I am speaking of the particle with its protective film of sodium resinate or other agent having a similar function. It is also understood that the particle of inert material surrounded by the protective agent undergoes no change in electrical charge, and its migration is due to the fact that the protective film carries the particle along with it.

The previously described rubber dispersion will resemble the so-called artificial lattices in which crude, reclaimed or vulcanized rubber is dispersed in water containing a protective agent. If, however, the protective agent is not one of the type herein described, that 1s, one which undergoes a change of electr cal charge depending upon whether the medium be alkaline or acid, a poor and uneven mechanical retention of the rubber will be obtained, since all of the particles, includingthe fibre, have approximately the same electrical charge. According to my discovery, art ficial lattices containing the proper protective agent can be made to deposit their rubber uniformly, quantitatively and firmly upon the fibres. Other materials which may be employed in the same manner are asphalt, graphite, synthetic resins, pine tar, p me pitch and other wood distillation products, eumar resin, paratfine, waxes, etc. Thesematerials I define as paper making ingredients, and I mean to include under this term those ingredients which are added to impart special properties to fibrous sheets, as for example waterproofncss, flexibility, pliability, 1ncreased electrical resistance, moldability. Instead of alum, I may use other acidic salts or acids themselves in the proper state of dilution in order to efiect the reversal of charge on the protective agent. I may also guarantee the alkalinity of the dispersion prior to reversal by adding a caustic alkali or ammonia.

Having thus described my invention, What I claim and desire to protect by Letters Patent is:

1. Process for making fibrous sheet material which comprises mixing a suspension of beaten fibres and a dispersion comprising rubber, Water, and a protective agent having a negative charge in alkaline medium, acidit'ying the mixture to reverse the charge on the protective agent, thus causing said agent to carry the dispersed rubber towards and onto the fibre, and subsequently forming into sheets.

2. Process for making fibrous sh'ect material which comprises mixing asuspension of beaten fibres and a dispersion containing rubber, water, and soluble compound of saponifiable acid having a negative charge in alkaline medium, acidifying the mixture to reverse the charge on the soluble compound, and causing it to carry the dispersed rubber towards and onto the fibre, and subsequently forming into sheets.

3. Process for making fibrous sheet material which comprises mixing a suspension of beaten fibres and a dispersion of paper making ingredients including rubber, water, and a protective agent comprising an alkali resinate, slowly acidifying the mixture thereby causing a reversal of electric charge on the resinate, allowing the positively charged resinate to carry the dispersed rubber towards and onto the negatively charged fibre, and

subsequently forming into sheet material.

4. Process for making fibrous sheet material which comprises mixing a suspension of beaten fibre and an alkaline dispersion containing rubber, water, and sodium resinate, acidifying the mixture, permitting the positively charged resinate to carry the dispersed rubber towards and onto the fibre, and subsequently forming into sheet material.

5. A process for making fibrous sheet maierial which comprises beating a paper making fibre in Water, adding an alkaline dispersion of rubber in water containing sodium resinate, mixing the suspension and the dispersion, slowly acidifying the mixture by the addition of alum solution, permitting the positively charged resinate thus formed to carry the dispersed rubber towards and onto the fibre, and subsequently forming into sheet material;

Signed at New York, county and State of New York, this 26th day of November, 1926.

'R-EED P. ROSE.

CERTIFICATE OF CORRECTION.

Patent No. 1, 675, 959.

Granted July 3, 1928, to

REED P. ROSE.

It is hereby certified that error-appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, line 75, before the word "carbon" insert the word "asphalt"; and that said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 14th day of August, A. D. 1928.

M. J. Moore, 

